Americans overwhelmingly approve of President Barack Obama’s use of drones to kill foreign terrorists, but fewer support the policy when the target is a U.S. citizen, according to a poll released Tuesday.

Seventy-one percent of Americans back the drone war, which began under President George W. Bush and was expanded under Obama. Only 20 percent oppose the program, according to the CBS News poll. Support is high across party lines — 78 percent of Republicans, 70 percent of Democrats and 68 percent of independents are supportive.

But Americans aren’t as certain about targeting U.S. citizens abroad who have become terrorists. A plurality, 49 percent support the program, and 38 percent oppose killing American terrorists. Fifty-eight percent of GOPers back the idea, along with 48 percent of Democrats and 45 percent of independents.

The highest level of opposition to the drone program comes from independents, not Democrats. A quarter of independents oppose the drone war, and 43 percent oppose targeting American citizens.

Drones have become a crucial part of the War in Afghanistan and the CIA’s covert war against terrorists in Yemen and Pakistan. The military launched an average of 33 drone strikes a month in Afghanistan in 2012.

A Department of Justice white paper drawn up to lay out the legal justification for the drone strike that killed Anwar Al-Awlaki, an American citizen working for Al Qaeda in Yemen, leaked early this month and drew outrage for civil libertarians.